This invention relates to methods and apparatus for the selective heating of lipid-rich tissue including sebaceous glands, subcutaneous fat, lipid in membranes of cells, and fat surrounding organs, vessels, hair bulbs, and other anatomical elements, and/or to the selective destruction or removal of such tissue and/or structures adjacent thereto; and more particularly to methods and apparatus for using optical radiation in selected wavebands, which radiation may be obtained from a laser or other suitable light source, to effect such heating, removal and/or destruction.
Adipose or lipid-rich tissue, which is also sometimes referred to as xe2x80x9cfatxe2x80x9d or xe2x80x9cfatty tissuexe2x80x9d, is a common cosmetic and surgical problem, and excessive body fat may also pose certain other health risks. Many factors, including heredity, glandular function, nutrition and lifestyle affect both the extent and location of body fat. Despite dieting and exercise, many people cannot lose fat, particularly in certain areas. Heretofore, liposuction, a procedure in which fat is removed by a suction cannula under local anesthesia, or other forms of fat excision have been used. Fat also occurs in pads on the face and neck and small area local liposuction has sometimes been performed in these areas. However, liposuction is an invasive surgical procedure and presents all of the disadvantages and risks to the patient involved in such a procedure, including scars at the sites of entry into skin. Another problem with liposuction is that it is not selective in only removing unwanted fat, but also rips out tissue in the path of the liposuction hose, including the collagen supporting structure holding the patient""s skin in place. This can result in cosmetically unattractive sagging skin in the treated area, in addition to significant pain to the patient both during and after the procedure, risk of infection and other potential problems. The trauma caused by extreme liposuction has in some cases even resulted in the death of the patient. Further, while liposuction can be used for the removal of deep fat, it is significantly less effective for removing fat at a superficial level of subcutaneous fat just below the dermis. Such removal is desirable in some cases because it is less traumatic to the patient. However, it is difficult to do with a liposuction cannula without scratching the dermis, damage to the dermis not healing readily, and attempts to perform surface liposuction also result in an uneven removal of fat which leaves an esthetically unattractive patterning on the patient""s skin. Therefore, while liposuction is still used extensively for the removal of excess fat, it is not a desirable procedure.
Fat is also a problem in various surgical procedures where it may be difficult to locate vessels, organs or other anatomical elements on which surgery is to be performed when these elements are covered in fat, and it may be difficult to close surgical openings in such elements. Performing surgery on vessels, organs or other elements covered by fat is therefore risky and current procedures for removing such fat to facilitate surgical procedures have significant limitations. Of particular concern is mesenteric fat which is a common hindrance in laparoscopic surgery. With the current trend of making surgical procedures less invasive by inserting tools through a small surgical opening, the removal of fat in the region where a surgical procedure is being performed, utilizing a tool consistent with such surgical procedures, so as to facilitate remote viewing of the anatomical element being treated/operated on is therefore becoming increasingly important.
In addition, a major problem for teenagers and others is acne which originates at least in part from obstruction of outflow from a sebaceous gland. Certain drug treatments for acne operate through a mechanism of decreasing sebaceous gland output. Destruction, removal, or unblocking of the sebaceous gland, which gland contains lipid-rich tissue, in a non-invasive manner are therefore desirable alternatives for treatment or prevention of acne.
Another related problem is the removal of unwanted hair, and in particular the long-term or permanent removal of such hair by the damage or destruction of the hair follicle. Many techniques have been employed over the years for this treatment, including electrolysis, waxing and treatments with various forms of radiation, including light. However, electrolysis is slow and both electrolysis and waxing are painful to the patient and seldom permanent. Various radiation treatments, particularly those involving light, work more effectively for patients having darker hair than for patients with light hair and various proposals have been made over the years to add a chromophore in some way to the follicle to facilitate such treatments. The use of such artificial chromphores has not heretofore been particularly successful.
Other related problems involve either removing fat, for example in the stratum corneum, under certain conditions, for example when a pressure injection is to be given, selectively porating cells having lipid-rich walls to permit substances, for example therapeutic agents, to enter the cells or to permit the removal of wanted or unwanted substances therefrom or to otherwise heat or destroy lipid-rich tissue for various therapeutic purposes.
While lasers or other light sources have been proposed in the past for heating, removal, destruction (for example killing), photocoagulation, eradication or otherwise treating (hereinafter collectively referred to as xe2x80x9ctreatingxe2x80x9d or xe2x80x9ctreatmentxe2x80x9d) of lipid-rich tissue such as subcutaneous fat, the lasers proposed for such procedures have operated at a wavelength where lipid-rich tissue has an absorption coefficient which is generally significantly less then than that for water. This presents several problems. First, lipid-rich tissue is radiation heated as a result of absorption in the tissue of radiation energy. Therefore, for wavelengths at which lipid-rich tissue does not absorb the radiation strongly, large amounts of energy must be applied to the tissue in order to obtain the requisite heating. However, in addition to significantly increasing the cost of the procedure, the need for high energy poses a danger of damage to surrounding tissue or the tissue through which the radiation passes, particularly since most such tissue is primarily composed of water which absorbs the radiant energy much more at these wavelengths.
This is a particular problem for subcutaneous fat which generally starts at a depth of at least 1 to 4 mm into a patient""s skin, and may be deeper for some individuals or some body areas. Therefore, in order for the radiation to target to the subcutaneous fat to cause selective heating or destruction thereof, it must pass through several millimeters of tissue formed primarily of water. Since water preferentially absorbs at these wavelengths, most of the incident radiation is absorbed in the skin prior to reaching the subcutaneous fat and, since skin is a scattering medium, incident light is also scattered and reflected from the patient""s skin, resulting in a very small fraction of the incident light reaching the subcutaneous fat. Therefore, due to both the small fraction of the applied energy reaching the subcutaneous fat and the low absorption of this energy by the fat, in order to get enough energy to the subcutaneous fat at these wavelengths to be effective, large amounts of radiation would need to be applied to the overlying epidermis and dermis. Since such high levels of radiation absorbed in the dermis or epidermis would cause significant thermal damage to these skin layers at the prior art wavelengths, treatment/destruction of fat cannot be performed through the skin, but must be performed by providing an opening, for example a surgical opening, through the skin to provide direct contact with the fat tissue to be treated. Even when the radiation is applied directly to the fat tissue to be treated, high energy is required and great care must be exercised to avoid excessive radiation of surrounding or underlying tissue so as to minimize damage thereto. Other prior art fat treatment techniques, involving the use of either microwaves or ultrasound, either alone or in conjunction with liposuction, to melt or loosen the fat and to remove it or have it absorbed into the body, have either proved not to be effective for fat removal, have posed potential health hazards to patients, either actual or perceived, or have still involved invasive procedures, the risk of which have been discussed earlier.
A need therefore exists for an improved technique for heating and destroying, or otherwise targeting lipid-rich tissue, including, but not limited to, subcutaneous fat, sebaceous gland, lipid in membrane cells and fat covering anatomical elements on which surgical or other procedures are is to be performed, which does not suffer the limitations of prior art techniques, including liposuction, and which is significantly more selective than the prior art in the destruction of lipid-rich tissue over tissue containing water so as to safely achieve the desired effects on lipid-rich tissue in performing a therapeutic procedure.
In accordance with the above, this invention provides a method and apparatus for selectively targeting lipid-rich tissue to effect a desired treatment, the method/apparatus involving irradiating the lipid-rich tissue at an infrared wavelength at which the ratio of absorption of the radiation by lipid-rich tissue to absorption by water is 0.5 or greater, and preferably greater than one. In particular the irradiation is preferably at a wavelength between 880-935 nm, 1150 to 1230 nm, 1690 to 1780 nm, or 2250 to 2450 nm with a fluence and for a duration sufficient to treat such lipid-rich tissue. For preferred embodiments, depending on application, the irradiation wavelength is between approximately, 900 to 930 nm, 1190 to 1220 nm, 1700 to 1730 nm, or 2280 to 2360 nm, with approximately 920 nm, 1210 nm, 1715 nm, and 2300 nm being most preferred wavelengths. While the fluence and duration of irradiation will vary somewhat with the patient undergoing treatment, the anatomical location of the tissues being treated, the radiation source and wavelength, the size of the lipid-rich tissue being treated and other factors, for preferred embodiments the treatment fluence may for example be approximately 0.5 J/cm2 to 500 J/cm2, with the duration of treatment pulses being approximately 10 xcexcs to several seconds, or even minutes for photothermal effect, and less than 1 xcexcs (i.e., generally 1 xcexcs to 1 ns) for photomechanical effects.
Where the lipid-rich tissue being treated is one or more sebaceous glands, irradiating the tissue/gland is performed by applying the energy at an indicated wavelength, which wavelength is preferably in one of the higher bands, to the skin surface overlying such one or more sebaceous glands. Where the lipid-rich tissue is subcutaneous fat, energy may be applied to the skin surface overlying the subcutaneous fat to be treated. Where either the sebaceous gland or subcutaneous fat is treated through the overlying skin, and particularly for subcutaneous fat, the radiation is preferably applied through an applicator which applies pressure to the skin above the lipid-rich tissue being treated. This pressure reduces the distance from the radiation-applying applicator to the lipid-rich tissue being targeted, removes blood from the area above the fat tissue being targeted and compresses such overlying tissue to reduce scattering and enhance optical focusing of radiation on the treatment area. It is also desirable that the skin above the area being treated be cooled to a selected depth, which depth is above that of the lipid-rich/fat tissue being targeted. Thus, cooling could be deeper for the treatment of subcutaneous fat, where the cooling could be most of the way through the dermis, while the cooling would be to a much shallower depth, perhaps only to the dermis/epidermis (DE) junction, where the sebaceous gland is being treated. While radiation in the higher bands can be used, and may be preferable because of the higher absorption coefficient of fat in these bands, for treating the sebaceous gland which is relatively close to the skin surface, absorption by water at these wavelengths make it difficult to reach subcutaneous fat, and radiation in the lower bands, for example in 1150 to 1230 nm range where water is less absorbent may therefore be preferable for treating subcutaneous fat. In addition to or instead of pressure being applied to the skin, a fold of skin may be drawn into a recess in a radiation delivery head in a suitable manner and radiation applied to the recess from at least two directions. This has a number of beneficial effects, including reducing the distance from the radiation source to the lipid tissue, increasing the radiation at the desired depth without increasing radiation in regions above the target area and, where a retroreflection technique to be discussed later is utilized, substantially eliminating radiation loss as a result of the scattered radiation reflected from the patient""s skin. Alternatively, to increase the local intensity for treatment of subcutaneous fat when delivered through the overlying skin, a convergent incident beam is advantageous to compensate for losses due to optical scattering and absorption in the dermis.
While the sebaceous gland may be heated to destroy the gland as part of an acne treatment, the sebaceous gland may also be heated to cause destruction of adjacent areas of a hair follicle, for example the stem cells of the hair follicle as a treatment to achieve hair removal and impede regrowth. Radiation in the indicated wavelengths may also be applied selectively to cells having lipid-rich membranes to porate the membranes to for example permit selective drug delivery to the cells or for other purposes for lipid-rich cells or tissue may be otherwise targeted and heated for affecting some other therapeutic function. Since the radiation fluence, pulse duration, wavelength and other factors may be carefully controlled, and the area to which the radiation is directed may also be controlled, selective lipid-rich cells may be non-invasively targeted to achieve the above and other therapeutic affects.
Where subcutaneous fat is being non-invasively treated, duration of radiation pulse and the temperature to which the fat or lipid tissue is heated are critical to the desired results. For example, at increased temperature, fat is altered by a biochemical reaction or lipolysis, while for higher temperatures and sufficient pulse duration, fat cells are killed, permitting the cells and liquid lipid therein to be absorbed. At still higher temperatures, cell membranes are destroyed, permitting lipid pools to be formed. These pools may also be absorbed but, since free fatty acid in lipid can be toxic in sufficient quantity, if substantial quantities of fat cell membranes have been destroyed, permitting a large lipid pool to be formed, it is preferable to remove the lipid, for example with a cannula or needle. The heated collagen of supporting structure may react to provide a more pleasing skin appearance after treatment and avoid sagging folds of skin or skin depressions where the lipid tissue has been destroyed. While all of the fat in a subcutaneous layer may be treated, it is difficult to get sufficient energy deep into the fat, so treatment is generally restricted to a surface layer of the fat. Repetitive treatments may be performed to remove successive layers of the subcutaneous fat.
While non-invasive procedures are preferable, subcutaneous fat may also be treated by passing a probe through the skin to the subcutaneous fat to be treated. The probe, which may for example be a needle, may be passed into the subcutaneous fat at an angle to the skin surface and the probe may be moved both in an out of the skin and rotated about its skin entry point to irradiate and treat subcutaneous fat over a selected area. This needle or probe may also contain a cannula for removing liquid lipid pooled as indicated above from the radiation treatment
Where lipid-rich tissue/fat surrounds a vessel, organ or other anatomical element on which a surgical or other procedure is to be performed, the irradiation may be performed by use of a tool which is in at least near contact, and preferably in contact, with the fat to be treated, the element treating the fat to expose the anatomical element on which the procedure is to be performed. Because radiation for this embodiment does not need to pass through water rich tissue to reach the fat, wavelengths in the higher bands would normally be used for this procedure.
While various light sources might be utilized to obtain optical energy within the required bands, and in particular at the preferred wavelengths, including a suitably filtered tungsten lamp, an optical parametric oscillator, a Raman convertor or shifter, a color center laser or a tunable dye laser, the preferred light source at the desired wavelengths is a diode laser or lasers with flashlamp or diode pumping which will be described in greater detail later.